CMP (“Chemical Mechanical Planarization” or “Chemical Mechanical Polishing”) processes are known in the art. CMP processes generally involve the removal of material from uneven topography on a substrate surface, typically a semiconductor-related substrate, until a planarized (i.e., flat) surface is created. The CMP process is used in connection with a polishing composition (or otherwise known as a sol or slurry) and polishing pad. The polishing composition typically contains abrasive particles dispersed in an alkaline solution or other liquid carrier. The polishing composition is applied to the substrate surface with the polishing pad, which is often saturated with the polishing composition. A rotating head presses the rotating substrate against the polishing pad to planarize or polish the substrate surface.
This CMP process combines a “mechanical” effect of smoothing with a abrasive particles with a “chemical” effect of etching with acidic or basic fluid solution. This provides greater accuracy in, for example, photolithography, allowing layers to be added with minimal and/or acceptable height variations.
In traditional CMP processes, a high silicon dioxide and a low silicon nitride removal rate are desired to minimize loss of the nitride film. The ratio of rate of removal of silicon dioxide to the rate of removal of silicon nitride is defined as “selectivity” or “selectivity ratio”. In contrast, there are now certain applications where the reverse, i.e., a high nitride and a low oxide removal rate, is desirable. Such reverse applications, however, have been difficult to achieve. (The ratio of rate of removal of silicon nitride to the rate of removal of silicon dioxide is defined as “reverse selectivity” or “reverse selectivity ratio”.)
The polishing compositions that contain dispersed abrasive particles in a liquid medium can also exhibit varying degrees of stability along a range of pH values, which can be established by measuring the zeta potential of the dispersion. The zeta potential indicates the degree of repulsion between same charged particles adjacent to one another in a dispersion. A colloid dispersion with a high zeta potential, either positive or negative, will confer stability, i.e. resist aggregation. A lower zeta potential will generally confer instability to the colloid dispersion where attraction exceeds repulsion, meaning the dispersion will tend to break and flocculate. Thus, colloids with high zeta potential (negative or positive) tend to be generally electrically stable while colloids with low zeta potential tend to aggregate or flocculate.
Accordingly, there is a need to provide an improved electrically stabilized polishing composition for use in CMP processes with high reverse selectivity, and methods thereof.